Miniature multistation photometer rotor temperature control

ABSTRACT

A rotor temperature monitoring and control circuit for a Miniature Fast Analyzer is provided. Radiant heat from a heat lamp is directed onto the rotor and, by means of a thermistor positioned in the rotor, closed-loop control of the rotor temperature is achieved. Temperatures within + OR - 0.2 degree centigrade can be maintained at the cuvettes of the rotor.

United States Patent [191 Johnson I v [451 Feb. 12, 1974.

[ MINIATURE MULTISTATION PHOTOMETER ROTOR TEMPERATURE CONTROL [75]lnventor: Wayne F. Johnson, Loudon, Tenn.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission, Washington, DC.

[22] Filed: Jan. 11, 1973 [21] Appl. No.: 322,645 1 [52] US. Cl 219/497,219/505, 219/506 [51] Int. Cl. H051) 1/02 [58] Field of Search 219/494,497, 499, 501, 505,

[56] References Cited UNITED STATES PATENTS Storke 219/497 X 2/19683,474,258 10/1969 Nagy 219/497 X 3,665,159 5/1972 Becker et al.....219/497 X 3,725,685 4/1973 Bourgoin et a1. 219/497 X PrimaryExaminer--Bernard A. Gilheany Assistant Examiner-F. E. Bell Attorney,Agent, or Firm John A. Horan [57 I ABSTRACT A rotor temperaturemonitoring and control circuit for a Miniature Fast Analyzer isprovided. Radiant heat from a heat lamp is directed onto the rotor and,by means of a thermistor positioned in the rotor, closed-loop control ofthe rotor temperature is achieved. Temperatures within i0.2 degreeCentigrade can be maintained at the cuvettes of the rotor. I

3 Claims, 1 Drawing Figure TEMP ADJ.

Seney 219/497 X 1 MINIATURE MULTISTATION PHOTOMETER ROTOR TEMPERATURECONTROL BACKGROUND OF'THE INVENTION filed Oct. 6, 1972, and having acommon assignee with the present application. The present invention wasconceived to be utilized with such a device.

Enzyme analyses are frequently performed by means of rotary cuvette-typeanalytical photometers. This kind of analysis ideally requires that thetemperature of the reacting solutions be controlled within less than onedegree centigrade. For example, control of the reaction temperaturewithin a few tenths of a degree can be more important than the selectionof the reaction temperature itself, which might be typically chosen as30C, 32C, or 37C.

With the ordinary size analyzers it has not been possible tosatisfactorily meet this temperature condition. Such an ordinary sizeanalyzer is described in US. Pat. No. 3,555,284,issued to a commonassignee on Jan. 12, 1971. The large mass of the rotor in such a priordevice implies slow heat transfer within the rotor and various internalheater arrangements utilizing the principle of conductive transfer ofheat have consistently resulted in slow thermal response. On the otherhand, the miniature rotor of the compact photometer of theabove-mentioned copending application due to its III small size wouldmake conduction heating with internal heaters very difficultif notimpossible. Thus, there exists a need for efficiently heating the rotorof a small compact photometer and for accurately maintaining thetemperature thereof at a desired operating temperature such that enzymeanalyses can be efficiently conducted.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide means, associated with the rotor of a compact analyticalphotometer of the rotary cuvette type, for sensing and regulating thetemperature of the rotor to maintain it at a desired temperature duringoperation of said BRIEF DESCRIPTION OF THE DRAWING The single FIGURE inthe drawing is a wiring diagram illustrating the temperature detectorsection and the temperature controller section of the presentinventlOll.

DESCRIPTION OF THE PREFERRED EMBODIMENT The miniaturized photometerdescribed in the abovementioned copending application includes a smalllowmass removable and disposable rotor primarily for the purpose ofminiaturization and low cost. With plastic being a preferredconstruction material for such a rotor, the small rotors have been ofsandwich construction wherein a black plastic disk having holestherethrough for defining the cuvettes is fixed between two clearplastic disks. The center disk is black in color so that the individualcuvette holes may be'discerned. The temperature of therotor is detectedby a thermistor that is positioned in the rotor alignment pin very nearone of the cuvettes, and the thermistor may be connected to a meter bymeans of a pair of slip rings in the same manner as described in theabove-mentioned copending application. This temperature detectionsystemhas been combined with a temperature control circuit in thepresent invention such that the temperature of the rotor may bemaintained at some desired temperature. Such a combined circuitry isillustrated in the single FIGURE in the drawing.

The temperature detector circuit consists of a thermistor 15 located inthe photometer rotor housing, not shown, and a calibration potentiometer17 connected in parallel between a current-to-voltage converter 18 and aSPDT switch 16 that is further connected to a 10V source. When theswitch 16 is in its normal position (READ) the thermistor 15 isconnected to the 10V source. In the other position (CAL), the switch 16connects the potentiometer 17 to the 10V source. Since the resistancevalue of every thermistor will be slightly different at the chosencontrol temperature, a calibration curve for each thermistor must beobtained to establish the resistance value at the control temperature.

The potentiometer 17 can be permanently set to this resistance value sothat with the switch 16 in the CAL position the potentiometer simulatesthe thermistor at the control temperature.

The final element in the detector section is a voltage amplifier 19 thatis connected to receive the output of the current-to-voltage converter18. Components 18 and 19 (which can be a dual operational amplifiersystem) function to slightly amplify the current signal from thethermistor l5 and change it to a voltage signal. The current-to-voltageconverter 18 includes a range (span) potentiometer 11, and the voltageamplifier 19 includes a zero suppression potentiometer 13 and anadditional span control potentiometer 12. These features enable a 50 uAmeter 20 to read full-scale a narrow temperature range of, for example,28 to 32 centigrade. The meter 20 is connected to the amplifier 19 byway of a current limiting resistor 21 and a switch The output of thevoltage amplifier 19, in addition to being connected to the meter 20, isalso connected as one of two inputs to a comparator 22 in thetemperature controller section of the present invention. The other inputto the comparator 22 is a signal of opposite polarity which is obtainedfrom a reference potentiometer 23 (TEMP ADJ). The referencepotentiometer 23 is preset to exactly nullify the detected temperaturesignal when the thermistor 15 is at the desired control temperature. Thesetting of the potentiometer 23 is accomplished. by turning the systemon and adjusting the potentiometer until the desired cuvette temperatureis obtained. A diode 24, a driver transistor 25, and a power transistor26 comprise a power amplifier wherein any difference in the inputvoltages to the comparator 22 is amplified by a factor of and a highcurrent output is then provided that is used to 3 power the radiant heatlamp 14 which is positioned adjacent to or in close proximity to thephotometer rotor, not shown, to supply heat thereto until such time asthe desired temperature is reached by the rotor as sensed by thethermistor 15.

There is thus provided a closed-loop radiant heat controller whereinradiant heat from the lamp 14 passes through a transparent rotor cover(not shown) and is rapidly absorbed by the black plastic of the rotor.The clear plastic of the rotor acts as an insulator to prevent heatloss, especially to the aluminum rotor holder, not shown. Evendistribution of heat is assured by the rotation of the rotor under theradiant light source.

This invention has been described by way of illustration rather thanlimitation and it should be apparent that it is equally applicable infields other than those described.

What is claimed is: v

1. In a compact analytical photometer of the rotary cuvette type, atemperature detector and control system for maintaining the rotor ofsaid photometer at a desired temperature comprising a thermistor mountedin said rotor near one of the cuvettes thereof, a positive voltagesource connected to said thermistor, a currentto-voltage converterconnected to the output of said thermistor, a voltage amplifierconnected to the output of said converter, a meter connected to saidamplifier for providing an indication of the temperature of said rotor,a comparator, a temperature-adjustment reference potentiometer, theoutput of said voltage amplifier and output of said potentiometerconnected in opposition to each other and as a combined input to saidcomparator, a radiant heat lamp positioned adjacent to said rotor forsupplying heat thereto, and means connected between the output of saidcomparator and the input to said lamp for amplifying any output signalfrom said comparator for powering said lamp as long as there is anydifference in the input voltages to said comparator, said referencepotentiometer adapted to be preset to exactly nullify the detectedtemperature signal from said thermistor when said rotor isat saiddesired temperature, whereby said system automatically maintains saidrotor at said desired temperature.

2. The system set forth in claim 1, and further including a calibrationpotentiometer connected in parallel with said thermistor between saidpositive voltage source and said converter, and asingle-pole-doublethrow switch for selectively connecting either saidcalibration potentiometer or said thermistor between said positivevoltage source and said converter.

3. The method of maintaining the temperature of the rotor cuvettes in arotary cuvette photometer at a desired value above ambient temperaturecomprising the steps of supplying radiant heat from a single source to arotor containing said cuvettes, detecting the temperature adjacent oneof said cuvettes, generating a first electrical signal proportional tosaid detected temperature, generating a second electrical signalproportional to the temperature desired to be maintained in saidcuvettes, generating a third electrical signal proportional to anydifference between said first and second signals, and controlling theradiant heat supplied to said rotor in accordance with said third signalto maintain said temperature at said desired value above the ambienttemperature to which said photometer is exposed.

1. In a compact analytical photometer of the rotary cuvette type, atemperature detector and control system for maintaining the rotor ofsaid photometer at a desired temperature comprising a thermistor mountedin said rotor near one of the cuvettes thereof, a positive voltagesource connected to said thermistor, a current-to-voltage converterconnected to the output of said thermistor, a voltage amplifierconnected to the output of said converter, a meter connected to saidamplifier for providing an indication of the temperature of said rotor,a comparator, a temperature adjustment reference potentiometer, theoutput of said voltage amplifier and output of said potentiometerconnected in opposition to each other and as a combined input to saidcomparator, a radiant heat lamp positioned adjacent to said rotor forsupplying heat thereto, and means connected between the output of saidcomparator and the input to said lamp for amplifying any output signalfrom said comparator for powering said lamp as long as there is anydifference in the input voltages to said comparator, said referencepotentiometer adapted to be preset to exactly nullify the detectedtemperature signal from said thermistor when said rotor is at saiddesired temperature, whereby said system automatically maintains saidrotor at said desired temperature.
 2. The system set forth in claim 1,and further including a calibration potentiometer connected in parallelwith said thermistor between said positive voltage source and saidconverter, and a single-pole-double-throw switch for selectivelyconnecting either said calibration potentiometer or said thermistorbetween said positive voltage source and said converter.
 3. The methodof maintaining the temperature of the rotor cuvettes in a rotary cuvettephotometer at a desired value above ambient temperature comprising thesteps of supplying radiant heat from a single source to a rotorcontaining said cuvettes, detecting the temperature adjacent one of saidcuvettes, generating a first electrical signal proportional to saiddetected temperature, generating a second electrical signal proportionalto the temperature desired to be maintained in said cuvettes, generatinga third electrical signal proportional to any difference between saidfirst and second signals, and controlling the radiant heat supplied tosaid rotor in accordance with said third signal to maintain saidtemperature at said desired value above the ambient temperature to whichsaid photometer is exposed.